Power transmission devices for transmitting power of engines of automobiles or the like to wheels thereof are each required to allow angular displacement for taking turns of the vehicle, as well as angular displacement and axial displacement that may be caused by bounds of the vehicle during the drive. Therefore, general drive shafts of automobiles or the like are each constructed of a plunging type constant velocity universal joint capable of allowing the angular displacement and the axial displacement, which is mounted on a differential side (inboard side), a fixed type constant velocity universal joint capable of forming a high operating angle, which is mounted on a driving wheel side (outboard side), and a shaft for coupling the two types of constant velocity universal joints to each other. Further, the above-mentioned fixed type constant velocity universal joint is coupled to a bearing device for a wheel, which rotatably supports the driving wheel.
In recent years, there has been a strong demand for higher fuel efficiency of automobiles, thereby arousing a strong desire to attain a lighter-weight bearing device for a wheel as one of the components of automobiles. Hitherto, various proposals have been made to attain a lighter-weight bearing device for a wheel. In addition to the light-weighting, another important factor is to reduce the cost by simplifying assembling or disassembling work in the location of assembling automobiles or the market of maintenance for automobiles.
A bearing device for a wheel as illustrated in FIG. 9 is a typical example of the bearing device that meets the demand described above. A bearing device 51 for a wheel is constructed so as to be integrated with a constant velocity universal joint 81 as a unit in a removable manner. The bearing device 51 for a wheel mainly includes an outer member 52, a hub wheel 53, an inner race 54, balls 55 as rolling elements, and a retainer 56. The outer member 52 has double-row outer raceway surfaces 57 and 57 formed on an inner circumference thereof, and a vehicle body mounting flange 52a integrally formed on an outer circumference thereof so that the bearing device 51 for a wheel may be mounted to a knuckle (not shown) of a vehicle body. The hub wheel 53 has a wheel mounting flange 58 integrally formed at one end portion thereof so that the wheel (not shown) may be mounted to the bearing device 51 for a wheel, an inner raceway surface 59 formed on an outer circumference thereof so as to be opposed to one of the double-row outer raceway surfaces 57 and 57 of the outer member 52, and a cylindrical small-diameter step portion 60 formed so as to extend from the inner raceway surface 59 in an axial direction. The inner race 54 is press-fitted to the small-diameter step portion 60, and an inner raceway surface 59 is formed on an outer circumference of the inner race 54 so as to be opposed to another of the double-row outer raceway surfaces 57 and 57 of the outer member 52. Further, an inner member 61 is formed of the hub wheel 53 and the inner race 54. The plurality of balls 55 and 55 are assembled into spaces between the double-row outer raceway surfaces 57 and 57 of the outer member 52 and the double-row inner raceway surfaces 59 and 59 of the inner member 61 in a rollable manner. The balls 55 are received in the retainer 56 at predetermined intervals in a circumferential direction. The inner race 54 is fixed in the axial direction by a staked portion 62 formed by plastically deforming an end portion of the small-diameter step portion 60 of the hub wheel 53 radially outward. Further, a face spline 63 is formed on an end surface of the staked portion 62.
Seals 65 and 66 are fitted to opening portions of annular spaces formed between the outer member 52 and the inner member 61 of the bearing device 51 for a wheel, to thereby prevent leakage of lubricating grease filled inside the bearing to the outside and entry of rainwater, dust, and the like from the outside into the bearing.
On the other hand, the constant velocity universal joint 81 is a so-called Rzeppa constant velocity universal joint, which mainly includes an outer joint member 82, an inner joint member 83, a cage 84, and torque transmitting balls 85. The outer joint member 82 includes a cup section 86, and a bottom section 87 formed integrally with the cup section 86. A female thread 88 is formed on the bottom section 87. A face spline 90 is formed on a shoulder portion 89 of the bottom section 87. The face spline 90 meshes with the face spline 63 formed on the end surface of the staked portion 62 of the hub wheel 53, to thereby transmit rotational torque from a drive shaft (not shown) to the wheel mounting flange 58 via the constant velocity universal joint 81 and the hub wheel 53.
Both the opposing face splines 90 and 63 of the outer joint member 82 of the constant velocity universal joint 81 and the hub wheel 53 of the bearing device 51 for a wheel are meshed with each other, and a fastening bolt 64 is threadedly engaged with the female thread 88 of the bottom section 87 of the outer joint member 82. With the fastening bolt 64, the bearing device 51 for a wheel and the constant velocity universal joint 81 are fixed to each other by fastening. With the structure of such a removable unit, a lighter-weight and more compact device can be attained, and the assembling or disassembling work is simplified. In Patent Literature 1, there is disclosed a method of forming the face spline of the bearing device for a wheel as described above.